In Plato we find, as we will later in Aristotle, a theory of literature which is a component part of a whole philosophical system. That is, Plato sets literature in the wider context of human activity in general. Still more, he sets literature in the frame of a general theory of reality. This theory we call Platonism, and it has been enormously influential. It is all the more alarming that it is from this higher viewpoint that Plato seems to condemn literature. For the first time, the theory of literature has been provided with an explicit philosophical basis, and the surprising result is the disparagement of literature. It has always seemed somewhat of a paradox that Plato, the most poetical of philosophers, who wrote his books in dialogue form and often uses myths and fables to explain his meaning, should be an enemy of poetry. This is nevertheless the case. However, this statement should be qualified. Plato does accept some kinds of poetry, and he was in spite of himself a great lover of poetry. Otherwise, he would not have feared it as he did, and would not have cared to warn against it.
Plato adapts in a single theory the teachings of Heraclitus and Parmenides, as well as the Pythagorean number theory. "Plato distinguishes between the continuous and boundless stuff of our sensory experience, and the indeterminate world of becoming, and a real or rational world of limit, that is, of ratios between both unit numbers and geometrical lines." The rational principle in man is called the logos , and it allows us access to the only real world beyond the false appearances of the material world: the realm of ideas, of pure concepts or essences. In Greek thought the opposition between limit and lack of limit is crucial: the idea, the essence, are limiting principles: they define things as they are, they give them a being and a form, whereas matter as such is chaos, lacking in structure when not penetrated by the Idea. We think of concepts or ideas as something which is in some way derived from our sensory experience of the material world. For Plato, it is the other way round: the ideas are the origin and the underlying structure of the material world. Mathematical entities are some way between the world of pure ideas and the world of sensory experience. The only adequate expression of ideas would be a mathematical expression. Mathematical relationships and forms are absolutely beautiful: art ought to be inspired by them and not by appearances.
Plato is an enemy of any kind of perspectivism in art, because perspective is a technique related to man's place in the material world: it shows things as they seem to be to an observer, and not as they actually are in themselves. Plato's age was one of subtle perspectival refinements in painting, sculpture and architecture, and of an increasing naturalism in art. Plato mistrusts this current tendency towards realism, and advocates stylization and formalization in art. Only pure forms can be beautiful, because only they are true and good. The identification of goodness, truth and beauty will be a characteristic of many idealistic theories of art throughout the history of criticism.
According to Plato, there are two ways to reach the realm of ideas. The first is that of the philosopher. The philosopher is the privileged person who learns that this world is a cave where we see only the shadows of true beings, and follows reason to get out of the cave and admire the realm of ideas, dazzling as the light of the sun (Republic VI). The other way to get out of the cave is that of the lover. The Platonic lover ascends a scale from bodily beauty not only to ideal beauty, but to the complete hierarchy of ideas (Symposium). Because beauty, truth and goodness are ultimately one, the lover becomes in the end a philosopher, so the two ways to the realm of ideas converge. Plato gives a tentative definition of the beautiful, restricted to the lower degrees of the scale: "beautiful" does not mean "convenient," "appropriate" or "useful" ; we call beatiful "that which is beneficially pleasurable through the senses of sight and hearing."
Let us remark that the way of beauty to the world of ideas is not meant to include artificial beauty, the beauty of works of art. There is not in original Platonic thought a way of the artist to the world of ideas; the way of beauty is the way of the lover. Plato does not recognize in art a way to knowledge: however, later neo-Platonists like Plotinus and Proclus do, probably because of an Aristotelian influence. The original Platonic conception has important consequences for the theory of literature: it means that the beauty of literature is more apparent than real --that it is not linked to truth or goodness --that literature, in sum, is often false and immoral, and therefore dangerous.
There are scattered references to poetry throughout all of Plato's dialogues. However, his most important discussions of literature are to be found in an early dialogue, Ion (ca. 390 BC ), and in a dialogue of maturity, the Republic (ca. 375 BC). A dialogue of Plato's old age, the Laws (ca. 335 BC), is also significant.